It is know to use sealing tapes for cable joints, such as those involving the splicing together of two cables wherein at least one of the cables is a paper-insulated lead cable (PILC) that transmits electric current at so-called “medium” voltages up to approximately 20,000 volts. The PILC has an inner conducting core made, for example, of twisted strands of a conducting metal. The inner conducting core is surrounded along a length of the cable by a cylindrical layer of insulating paper that is impregnated with an oil. The layer of insulating paper is in turn surrounded along the length of the cable by an outer conductive jacket or sleeve made, for example, of lead or other conducting material. The layer of insulating paper acts as a dielectric that insulates the inner conductor from the outer conductive jacket. Although PILCs are rarely manufactured nowadays, many tens of thousands of meters of the cable type remain in service around the world. Therefore, a need remains for connecting the PILCs together and for connecting the PILCs to other types of cable.
In the PILCs, if migration of the oil occurs, the dielectric effect of the layer of insulating paper diminishes dramatically as the paper dries out. Generally this migration effect does not occur over the length of the cable that lies away from the cable ends; however, when an end of the PILC is spliced, a potential problem arises in that leakage paths exist for the oil.
One method of solving this problem is to enclose the cable joint with a rigid casing that includes a plurality of seals, such as the kind described in GB 1 485 613. The seals prevent deleterious migration of the oil from the paper layer. However, the arrangement of GB 1 485 613 is complicated. Not only does this arrangement make the cable joint expensive to manufacture, but also the assembly of the cable joint is a lengthy process that includes specific steps that must be completed in the correct order in order to assure leak-proofing of the cable joint. If the cable joint is assembled in a “field” situation by an inexperienced fitter therefore there is a danger of the steps not being completed correctly or in the correct order, such that the cable joint fails in service. Similarly if even one of the many components of the GB 1 485 613 cable joint becomes lost or damaged the integrity of the cable joint is compromised.
A further problem with the cable joint of GB 1 485 613 is that it does not seek to address the problems that can arise when the heating effect of electrical resistance in the cable of the PILC causes expansion of the oil in the layer of insulating paper. Under such circumstances the pressure of the oil within the cable joint can rise sufficiently that the oil is forced to leak out. High oil pressures can also arise when the cable joint is, for example, on a hillside, wherein a hydraulic head of oil above the cable joint can be adequate to promote the above-described migration of oil.
U.S. Pat. No. 5,374,784 proposes an arrangement in which the cable joint between two conducting elements of cables that are spliced together are encircled by an elastomeric sleeve. A heat-recoverable sleeve, for example, a sleeve made of a material that is pre-stressed to a shape that on heating reverts to a relaxed or recovered state that differs in shape from the pre-stressed shape, is used to surround the elastomeric sleeve. On heating the heat-recoverable sleeve shrinks to encircle the elastomeric member sufficiently tightly so that oil can not migrate into its interstices. Consequently, the oil can not enter into the material of the sleeve and a known effect of degradation of the sleeve does not, according to the disclosure of U.S. Pat. No. 5,374,784, occur.
However, the arrangement of U.S. Pat. No. 5,374,784 suffers from several disadvantages. First, the effect of the heat-recoverable sleeve is only of benefit while the pressure of the oil remains low. At higher pressures, the oil can force the elastomeric sleeve away from the cable joint and create voids. The oil can migrate into the voids and thereby cause failure of the insulation. Second, it is necessary for anyone fitting the cable joint of U.S. Pat. No. 5,374,784 in a “field” situation to carry a source of heat for heating the heat-recoverable sleeve. The need to carry such equipment has safety ramifications and generally complicates the process of creating the cable joint.
Further, JP 2000236619 discloses an arrangement in which an aluminum tape is used in conjunction with a complex structure in order to block oil leakage paths in the cable joint. A defect of this arrangement is that it is almost entirely rigid. Hence, it does not allow for small movements of the parts of the cable joint without the integrity of the cable joint becoming compromised. This in turn leads to failure of the dielectric layer in service.